Tungsten-halogen lamps, because of their superior performance characteristics, are being carefully considered by various lamp manufacturers as a possible replacement for Edison-type lamps for general lighting purposes. A major impediment in the path of providing a feasible tungsten-halogen replacement is the problem of short lamp life. A tungsten-halogen lamp having a power rating of 150 watts or less and operating with approximately 120 volts of alternating current requires a lamp filament with a relatively thin diameter in order to attain reasonable luminous efficacy.
In experimental low-wattage line-voltage lamps constructed under the existing art, the fine-wire filament is readily attacked by the halogen in the fill causing premature lamp failure and unacceptably short lamp life.
The tungsten-halogen regenerative cycle is well known. In lamps having a fill comprising a halogen and hydrogen, it is known that permeation of hydrogen through the envelope walls has a detrimental effect on lamp life. As the hydrogen diffuses through the walls, more of the halogen becomes free to attack and corrode the cooler portions of the lamp filament and other internal lamp parts. This corroding effect eventually destroys the lamp filament, usually at the ends of the filament or near the filamentary supports.
The corrosion problem is particularly acute in circumstances where fine-wire filaments are desired. A fine-wire filament will be destroyed more rapidly by corrosion because of its small mass per unit of length.
There is no low-wattage line-voltage tungsten-halogen lamp for general lighting purposes presently available in the consumer market. The inability to overcome the problem of corrosion and rapid destruction of a thin-wire filament is a major impediment in the path of developing a feasible replacement for the standard Edison-type lamp.